Resin-sealed type semiconductor device

ABSTRACT

A semiconductor device includes (a) a printed wiring board, (b) a semiconductor chip mounted on the printed wiring board, (c) a molded resin formed on the printed wiring board, covering the semiconductor chip therewith, and (d) at least one metal wiring formed on the printed wiring board and extending externally beyond the molded resin. The metal wiring is plated with a metal having a small adhesion force with the molded resin. An interfacial surface between the metal and the molded resin acts as a path through which moisture contained in the semiconductor device escapes outside when the semiconductor device is heated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a semiconductor device, and moreparticularly to a so-called sealed type semiconductor device in which asemiconductor chip mounted on a printed wiring board is sealed with amolded resin.

[0003] 2. Description of the Related Art

[0004] An example of a conventional sealed type semiconductor device isillustrated in FIGS. 1A to 1C. FIG. 1A is a top plan view of aconventional sealed type semiconductor device 100, FIG. 1B is across-sectional view taken along the line B-B in FIG. 1A, and FIG. 1C isa cross-sectional view taken along the line C-C in FIG. 1A.

[0005] As illustrated in FIGS. 1A to 1C, the conventional sealed typesemiconductor device 100 is comprised of a printed wiring board 101 onwhich wirings are formed in a predetermined pattern, a mount 102 fixedon a surface of the printed wiring board 101, a semiconductor chip 103mounted on the mount 102, a plurality of bonding pads 104 formed onupper and lower surfaces of the printed wiring board 101 forelectrically connecting the printed wiring board 101 to an externalcircuit therethrough, a molded resin 105 formed on the printed wiringboard 101, covering the semiconductor chip 103 therewith, and aplurality of boding wires 106 through which electrodes formed on thesemiconductor chip 103 are electrically connected to the bonding pads104.

[0006] Before a semiconductor chip is sealed with a resin, thesemiconductor chip is mounted on a lead frame, and then, electrodes ofthe semiconductor chip are electrically connected to inner leads throughbonding wires. When the semiconductor chip is sealed with a resin, aresin containing filler is usually selected.

[0007] In order to equalize a coefficient of thermal expansion of aresin to a coefficient of thermal expansion of a lead frame, afiller-containing resin is designed to contain filler materials having asmaller coefficient of thermal expansion than that of a resin to therebyreduce a coefficient of thermal expansion of the filler-containingresin.

[0008] When the semiconductor chip 103 is mounted on the printed wiringboard 101 and the semiconductor chip 103 is sealed with the resin 105like the semiconductor device 100 illustrated in FIGS. 1A to 1C, if thesemiconductor device 103 were an optic semiconductor chip, it would benecessary to use a transparent resin as the resin 105 in order to allowa light to reach the optic semiconductor chip.

[0009] A semiconductor device including such an optic semiconductor chipcould have reduced reliability relative to a semiconductor deviceincluding a semiconductor chip sealed with a filler-containing resin.

[0010] In general, filler is not mixed to a transparent resin. This isbecause if filler were mixed to a transparent resin, an index ofrefraction of the transparent resin would be changed, resulting in thata light incident to an optic semiconductor device would be fluctuated inan amount, and that it might not be possible to direct a light to atarget position on an optic semiconductor chip.

[0011] Since a transparent resin does not contain filler for theabove-mentioned reasons, a transparent resin could not have a~smallcoefficient of thermal expansion unlike that of a filler-containingresin, and would contain much moisture in comparison with afiller-containing resin.

[0012] In addition, since a resin has a high coefficient of thermalexpansion, a gap is likely to be formed between, a resin and a metalwire or between a resin and a substrate, resulting in that moisture isunavoidably residual in such a gap.

[0013] Thus, since the molded rein 105 has high hydroscopic property andfurther has a high coefficient of thermal expansion, it would beunavoidable for the semiconductor device 100 to contain moisture 107 tosome degree, as illustrated in FIG. 2A.

[0014] A substrate is often coated with a solder resist in order toprevent solder from adhering to the substrate. Since the molded resin105 and such a substrate have high adhesion force with each other, itwould be quite difficult for the moisture 107 to escape out of thesemiconductor device 100.

[0015] If a re-flow step is carried out while the semiconductor device100 contains the moisture 107, for instance, since the moisture 107could not escape out of the semiconductor device 100, the moisture 107would expand in the semiconductor device 100, resulting in a problemthat the semiconductor device 100 is cracked or peeled off as indicatedwith a reference number 108 in FIG. 2B.

[0016] For instance, such a crack directs to an inside of the moldedresin 105 from the resin and the metal wire, such a crack directs to aninside of the molded resin 105 from the resin and the substrate, theresin and the metal wire are peeled off each other, or the resin and thesubstrate are peeled off each other.

[0017] Japanese Unexamined Patent Publication No. 6-45496 (A) hassuggested a semiconductor device including a stage on which asemiconductor chip is mounted is formed integral with a frame through aplurality of support bars, and a metal conductor comprised of leadsarranged around the stage and packaged with a molded resin, wherein eachof the support bars has an increased width at which the support bar isconnected to the stage, and has a reduced width at which the support baris connected to the frame.

[0018] Japanese Unexamined Patent Publication No. 9-129808 (A) hassuggested a resin-sealed type semiconductor device including an islandon which a semiconductor chip is mounted, a plurality of terminal leadsincluding inner and outer leads, and a wing lead extending from theisland for allowing moisture contained in a resin to escape out of thesemiconductor device. The wing lead is formed on a plane different froma plane on which the terminal leads are arranged.

[0019] However, the above-mentioned Publications cannot solve theproblem mentioned earlier.

SUMMARY OF THE INVENTION

[0020] In view of the above-mentioned problem in the conventionalsemiconductor device, it is an object of the present invention toprovide a sealed type semiconductor device including a semiconductorchip mounted on a printed wiring board and sealed with a molded resin,which semiconductor device is capable of preventing occurrence of crackand/or peeling off therein, even if the semiconductor device is subjectto a heating step such as a re-flow step.

[0021] In one aspect of the present invention, there is provided asemiconductor device including (a) a printed wiring board, (b) asemiconductor chip mounted on the printed wiring board, (c) a moldedresin formed on the printed wiring board, covering the semiconductorchip therewith, and (d) at least one metal wiring formed on the printedwiring board and extending externally beyond the molded resin, the metalwiring being plated with a metal having a small adhesion force with themolded resin, wherein an interfacial surface between the metal and themolded resin acts as a path through which moisture contained in thesemiconductor device escapes outside when the semiconductor device isheated.

[0022] In the semiconductor device in accordance with the presentinvention, at least one metal wiring which is not used as an electricalconnector or which is used also as an electrical connector is formed toextend externally beyond the molded resin. The metal wiring is plated atits surface with a first metal having a small adhesion force with themolded resin. Hence, an interfacial surface between the first metal andthe molded resin can act as a path through which moisture passes.Accordingly, when a semiconductor device is heated in a step such as are-flow step, and hence, moisture contained in the semiconductor deviceexpands, the expanding moisture goes forward through the interfacialsurface between the first metal and the molded resin, and then,discharged externally of the semiconductor device. In accordance withthe semiconductor device, unlike the conventional sealed typesemiconductor device, it would be possible to allow moisture containedin the semiconductor device to escape externally of the semiconductordevice, and hence, prevent the semiconductor device from internallycracking and/or peeling off which would be caused by expansion ofmoisture contained in the semiconductor device.

[0023] There is further provided a semiconductor device including (a) aprinted wiring board, (b) a semiconductor chip mounted on the printedwiring board, and (c) a molded resin formed on the printed wiring board,covering the semiconductor chip therewith, wherein the printed wiringboard is formed with at least one through-hole, the through-hole isfilled with the molded resin or another resin with the through-holebeing plated at an inner wall thereof with a metal having a smalladhesion force with the molded resin or the another resin, and aninterfacial surface between the metal and the molded resin or theanother resin acts as a path through which moisture contained in thesemiconductor device escapes outside when the semiconductor device isheated.

[0024] In the semiconductor device in accordance with the presentinvention, the printed wiring board is formed with at least onethrough-hole. The through-hole is plated at its inner wall with a secondmetal having a small adhesion force with the molded resin or anotherresin filling the through-hole therewith. Under such circumstance, thethrough-hole is filled with the molded resin or the another resin.Hence, an interfacial surface between the second metal and the moldedresin or the another resin can act as a path through which moisturepasses. Accordingly, when a semiconductor device is heated in a stepsuch as a re-flow step, and hence, moisture contained in thesemiconductor device expands, the expanding moisture goes forwardthrough the interfacial surface between the second metal and the moldedresin or the another resin, and then, discharged externally of thesemiconductor device. In accordance with the semiconductor device,unlike the conventional sealed type semiconductor device, it would bepossible to allow moisture contained in the semiconductor device toescape externally of the semiconductor device, and hence, prevent thesemiconductor device from internally cracking and/or peeling off whichwould be caused by expansion of moisture contained in the semiconductordevice.

[0025] The above-mentioned at least one metal wiring may be comprised ofa metal wiring formed in a region where a solder resist is not formedand plated with a metal. A solder resist may be formed in a region otherthan a region where the metal wiring is formed.

[0026] When a metal wiring formed on a printed wiring board is platedwith a metal, a solder resist is first coated in a region which is notto be plated, and then, a metal wiring formed on a printed wiring boardin a region where a solder resist is not coated is plated with a metal.The above-mentioned at least one metal wiring may be formed by thisprocess. Specifically, there is determined a first region where a metalwiring is to be formed, apart from a region where a solder resist is tobe coated. The thus determined first area is not coated with a solderresist, but plated with a metal. As a result, an interfacial surfacebetween the molded resin and a metal plating layer coated around themetal wiring can act as a path through which moisture contained in thesemiconductor device escapes externally of the semiconductor device.

[0027] As a metal having a small adhesion force with a resin, there maybe selected a noble metal. It is preferable to select gold among a noblemetal. In place of gold, there may be selected platinum or palladium.

[0028] As an alternative, a metal having a small adhesion force with aresin is not to be limited to a noble metal. Any metal may be used, ifit has a small adhesion force with a resin.

[0029] There is still further provided a semiconductor device including(a) a printed wiring board, (b) a semiconductor chip mounted on theprinted wiring board, and (c) a molded resin formed on the printedwiring board, covering the semiconductor chip therewith, wherein theprinted wiring board has a first area in which a solder resist is notformed, the first area is formed such that a metal wiring formed in thefirst area and plated with a metal extends externally beyond the moldedresin, and an interfacial surface between the metal wiring and themolded resin acts as a path through which moisture contained in thesemiconductor device escapes outside when the semiconductor device isheated.

[0030] As mentioned earlier, when a metal wiring formed on a printedwiring board is plated with a metal, a solder resist is first coated ina region which is not to be plated, and then, a metal wiring formed on aprinted wiring board in a region where a solder resist is not coated isplated with a metal. By forming the metal wiring plated with a metal toextend externally beyond the molded resin, without coating with a solderresist, there can be formed a path through which moisture contained inthe semiconductor device escapes externally of the semiconductor device.Specifically, there is determined a first region where a metal wiring isto be formed, apart from a region where a solder resist is to be coated.The thus determined first area is not coated with a solder resist, butplated with a metal. As a result, an interfacial surface between themolded resin and a metal plating layer coated around the metal wiringcan act as a path through which moisture contained in the semiconductordevice escapes externally of the semiconductor device.

[0031] Since a solder resist is composed of a resin similar to themolded resin, such as epoxy, an adhesion force between a solder resistand the molded resin is quite higher than an adhesion force between themolded resin and a metal plating layer. An adhesion force between themolded resist and a metal wiring (for instance, composed of copper)coated with a solder resist, but not plated with a metal is higher thanan adhesion force between the molded resin and a metal plating layer.

[0032] In contrast, an adhesion force between a metal plating layer (forinstance, composed of gold) with which a metal wiring is plated, and themolded resin is relatively small. That is, both of an adhesion forcebetween a solder resist and the molded resin and an adhesion forcebetween the molded resist and a metal wiring coated with a solderresist, but not plated with a metal are higher than an adhesion forcebetween a metal plating layer with which a metal wiring is plated, andthe molded resin. Accordingly, when moisture contained in thesemiconductor device is, to escape externally of the semiconductordevice, the moisture passes through an interfacial surface where a smalladhesion force exists, namely, an interfacial surface between a metalplating layer with which a metal wiring is plated, and the molded resin.

[0033] The present invention is based on this discovery. When asemiconductor device is heated in a step such as a re-flow step, andhence, moisture contained in the semiconductor device expands, theexpanding moisture goes forward through an interfacial surface between ametal plating layer with which a metal wiring is plated, and the moldedresin, and then, discharged externally of the semiconductor device. Inaccordance with the semiconductor device, unlike the conventional sealedtype semiconductor device, it would be possible to allow moisturecontained in the semiconductor device to escape externally of thesemiconductor device, and hence, prevent the semiconductor device frominternally cracking and/or peeling off which would be caused byexpansion of moisture contained in the semiconductor device.

[0034] As mentioned earlier, a transparent resin does not contain fillermaterial having a smaller coefficient of thermal expansion than that ofa resin, and hence, tends to contain moisture. In accordance with thepresent invention, even if such a transparent resin is used as a moldedresin, it would be possible to allow moisture contained in thesemiconductor device to escape externally of the semiconductor device,and hence, prevent the semiconductor device from internally crackingand/or peeling off which would be caused by expansion of moisturecontained in the semiconductor device.

[0035] There is yet further provided a semiconductor device including(a) a printed wiring board, (b) a semiconductor chip mounted on theprinted wiring board, (c) a molded resin formed on the printed wiringboard, covering the semiconductor chip therewith, and (d) at least onemetal wiring formed on the printed wiring board and extending externallybeyond the molded resin, the metal wiring being plated with a firstmetal having a small adhesion force with the molded resin, wherein theprinted wiring board is formed with at least one through-hole, thethrough-hole is filled with the molded resin or another resin with thethrough-hole being plated at an inner wall thereof with a second metalhaving a small adhesion force with the molded resin or the anotherresin, and an interfacial surface between the first metal and the moldedresin and an interfacial surface between the second metal and the moldedresin or the another resin act as paths through which moisture containedin the semiconductor device escapes outside when the semiconductordevice is heated.

[0036] In the semiconductor device in accordance with the presentinvention, at least one metal wiring which is not used as an electricalconnector or which is used also as an electrical connector is formed toextend externally beyond the molded resin. In addition, the printedwiring board is formed with at least one through-hole. The through-holeis plated at its inner wall with a second metal having a small adhesionforce with the molded resin or another resin filling the through-holetherewith. That is, the above-mentioned semiconductor device is designedas a combination of the firstly mentioned semiconductor device and thesecondly mentioned semiconductor device. Hence, in accordance with thesemiconductor device, unlike the conventional sealed type semiconductordevice, it would be possible to allow moisture contained in thesemiconductor device to escape externally of the semiconductor device,and hence, prevent the semiconductor device from internally crackingand/or peeling off which would be caused by expansion of moisturecontained in the semiconductor device, similarly to the firstly andsecondly mentioned semiconductor devices.

[0037] There is still yet further provided a semiconductor deviceincluding (a) a printed wiring board, (b) a semiconductor chip mountedon the printed wiring board, and (c) a molded resin formed on theprinted wiring board, covering the semiconductor chip therewith, whereinthe printed wiring board has a first area in which a solder resist isnot formed, the first area is formed such that a metal wiring formed inthe first area and plated with a metal extends externally beyond themolded resin, the printed wiring board is formed with at least onethrough-hole, the through-hole is filled with the molded resin oranother resin with the through-hole being plated at an inner wallthereof with a second metal having a small adhesion force with themolded resin or the another resin, and an interfacial surface betweenthe metal and the molded resin and an interfacial surface between thesecond metal and the molded resin or the another resin act as pathsthrough which moisture contained in the semiconductor device escapesoutside when the semiconductor device is heated.

[0038] In the semiconductor device, there is determined a first regionwhere a metal wiring is to be formed, apart from a region where a solderresist is to be coated. The thus determined first area is not coatedwith a solder resist, but plated with a metal. As a result, aninterfacial surface between the molded resin and a metal plating layercoated around the metal wiring can act as a path through which moisturecontained in the semiconductor device escapes externally of thesemiconductor device, similarly to the thirdly mentioned semiconductordevice.

[0039] In addition, the printed wiring board is formed with at least onethrough-hole. The through-hole is plated at its inner wall with a secondmetal having a small adhesion force with the molded resin or anotherresin filling the through-hole therewith. That is, the above-mentionedsemiconductor device is designed as a combination of the firstlymentioned semiconductor device, the secondly mentioned semiconductordevice and the thirdly mentioned semiconductor device. Hence, inaccordance with the semiconductor device, unlike the conventional sealedtype semiconductor device, it would be possible to allow moisturecontained in the semiconductor device to escape externally of thesemiconductor device, and hence, prevent the semiconductor device frominternally cracking and/or peeling off which would be caused byexpansion of moisture contained in the semiconductor device, similarlyto the firstly, secondly and thirdly mentioned semiconductor devices.

[0040] The above and other objects and advantageous features of thepresent invention will be made apparent from the following descriptionmade with reference to the accompanying drawings, in which likereference characters designate the same or similar parts throughout thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1A is a top plan view of a conventional sealed typesemiconductor device.

[0042]FIG. 1B is a cross-sectional view taken along the line B-B in FIG.1A.

[0043]FIG. 1C is a cross-sectional view taken along the line C-C in FIG.1A.

[0044]FIG. 2A is a cross-sectional view of a conventional sealed typesemiconductor device.

[0045]FIG. 2B is a cross-sectional view of a conventional sealed typesemiconductor device including a cracked molded resin.

[0046]FIG. 3A is a top plan view of a sealed type semiconductor devicein accordance with the first embodiment of the present invention.

[0047]FIG. 3B is a cross-sectional view taken along the line B-B in FIG.3A.

[0048]FIG. 3C is a cross-sectional view taken along the line C-C in FIG.3A.

[0049]FIG. 4 is an enlarged side view of the semiconductor device inaccordance with the first embodiment of the present invention.

[0050]FIG. 5A is a cross-sectional view of the semiconductor device inaccordance with the first embodiment of the present invention,illustrating how moisture contained in a molded resin behaves when thesemiconductor device is heated.

[0051]FIG. 5B is a cross-sectional view of the semiconductor device inaccordance with the first embodiment of the present invention,illustrating how moisture contained in a molded resin behaves when thesemiconductor device is heated.

[0052]FIG. 6A is a top plan view of a sealed type semiconductor devicein accordance with the second embodiment of the present invention.

[0053]FIG. 6B is a cross-sectional view taken along the line B-B in FIG.6A.

[0054]FIG. 6C is a cross-sectional view taken along the line C-C in FIG.6A.

[0055]FIG. 7 is an enlarged view of an encircled portion X in FIG. 6B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] Preferred embodiments in accordance with the present inventionwill be explained hereinbelow with reference to drawings.

[0057] [First Embodiment]

[0058] A resin-sealed type semiconductor device in accordance with thefirst embodiment is illustrated in FIGS. 3A to 3C. FIG. 3A is a top planview of the semiconductor device, FIG. 3B is a cross-sectional viewtaken along the line B-B in FIG. 3A, and FIG. 3C is a cross-sectionalview taken along the line C-C in FIG. 3A.

[0059] As illustrated in FIGS. 3A to 3C, the resin-sealed typesemiconductor device 10 in accordance with the first embodiment iscomprised of a printed wiring board 11 on which wirings are formed in apredetermined pattern, a mount 12 fixed on a surface of the printedwiring board 11, a semiconductor chip 13 fixedly mounted on the mount12, a plurality of bonding pads 14 formed on upper and lower surfaces ofthe printed wiring board 11 for electrically connecting the printedwiring board 11 to an external circuit therethrough, a transparentmolded-resin 15 formed on the printed wiring board 11, covering thesemiconductor chip 13 therewith, and a plurality of boding wires 16through which electrodes formed on the semiconductor chip 13 areelectrically connected to the bonding pads 14.

[0060] In the first embodiment, the transparent molded-resin 15 iscomposed of epoxy.

[0061] The resin-sealed type semiconductor device 10 in accordance withthe first embodiment is designed to further include metal wirings 17 a,17 b, 17 c and 17 d formed on the printed wiring board 11. The metalwirings 17 a to 17 d are not used as an electrical connector.

[0062] Specifically, as illustrated in FIG. 3A, a rectangularchip-mounting area 18 in which the semiconductor chip 13 is to bemounted is formed centrally of the printed wiring board 11 as a metalpattern, and the metal wirings 17 a, 17 b, 17 c and 17 d extend towardsan outer edge of the printed wiring board 11 in parallel with oneanother from four corners of the chip-mounting area 18. The metalwirings 17 a, 17 b, 17 c and 17 d extend beyond the transparentmolded-resin 15, and reach an outer edge of the printed wiring board 11.Since the metal wirings 17 a, 17 b, 17 c and 17 d are formed extendingbeyond the transparent molded-resin 15, they are in atmospheric air atdistal ends thereof.

[0063] As illustrated in FIG. 4, each of the metal wirings 17 a, 17 b,17 c and 17 d is plated, that is, coated with a gold plating layer 19.

[0064] An adhesion force between the gold plating layer 19 coating themetal wirings 17 a, 17 b, 17 c and 17 d therewith and the transparentmolded-resin 15 is relatively small. In other words, the gold platinglayer 19 and the transparent molded-resin 15 make contact with eachother through such an adhesion force that moisture can pass through asmall gap formed between the gold plating layer 19 and the transparentmolded-resin 15.

[0065] Thus, an interfacial surface between the gold plating layer 19and the transparent molded-resin 15 acts as a path through whichmoisture can pass.

[0066] Accordingly, when the semiconductor device 10 is heated in a stepsuch as a re-flow step and hence moisture 20 contained in thesemiconductor device 10 expands, as illustrated in FIG. 5A, theexpanding moisture 20 goes forward along an interfacial surface betweenthe gold plating layer 19 and the transparent molded-resin 15, and then,discharged externally of the semiconductor device 10, as illustrated inFIG. 5B.

[0067] The inventors had conducted the experiments as follows in orderto ensure the semiconductor device 10 in accordance with the firstembodiment was not cracked and/or peeled off.

[0068] The inventors had fabricated both of the conventionalsemiconductor device 100 illustrated in FIGS. 1A to 1C and thesemiconductor device 10 in accordance with the first embodiment,illustrated in FIGS. 3A to 3C, by the same number, and measured a rate Rat which the semiconductor devices 100 and 10 were cracked and/or peeledoff after carrying out a re-flow step.

[0069] The results are shown in Table 1. TABLE 1 RATE R SemiconductorDevice 100 (Conventional) 41.7% Semiconductor Device 10 (FirstEmbodiment) 3.3%

[0070] As is obvious in view of Table 1, the semiconductor device 10 inaccordance with the first embodiment is not cracked and peeled off at ahigher rate than the conventional semiconductor device 100.

[0071] As having been explained so far, the resin-sealed typesemiconductor device 10 in accordance with the first embodiment allowsthe moisture contained in the semiconductor device 10 to escapeexternally of the semiconductor device 10, and can avoid from beingcracked due to the expansion of the moisture 20 contained in thesemiconductor device 10.

[Second Embodiment]

[0072] A resin-sealed type semiconductor device in accordance with thesecond embodiment is illustrated in FIGS. 6A to 6C and 7. FIG. 6A is atop plan view of the semiconductor device, FIG. 6B is a cross-sectionalview taken along the line B-B in FIG. 6A, FIG. 6C is a cross-sectionalview taken along the line C-C in FIG. 6A, and FIG. 7 is an enlarged viewof an encircled portion X in FIG. 6B.

[0073] As illustrated in FIGS. 6A to 6C, the resin-sealed typesemiconductor device 30 in accordance with the second embodiment iscomprised of a printed wiring board 31 on which wirings are formed in apredetermined pattern, a mount 32 fixed on a surface of the printedwiring board 31, a semiconductor chip 33 fixedly mounted on the mount32, a plurality of bonding pads 34 formed on upper and lower surfaces ofthe printed wiring board 31 for electrically connecting the printedwiring board 31 to an external circuit therethrough, a transparentmolded-resin 35 formed on the printed wiring board 31, covering thesemiconductor chip 33 therewith, and a plurality of boding wires 36through which electrodes formed on the semiconductor chip 33 areelectrically connected to the bonding pads 34.

[0074] In the second embodiment, the transparent molded-resin 35 iscomposed of epoxy.

[0075] In the semiconductor device 30 in accordance with the secondembodiment, as illustrated in FIG. 6A, the printed wiring board 31 isformed centrally with an almost rectangular chip-mounting area 37 inwhich the semiconductor chip 33 is to be mounted. As illustrated inFIGS. 6A and 6B, through-holes 38 are formed throughout the printedwiring board 31 in the vicinity of four corners of the chip-mountingarea 37.

[0076]FIG. 7 is an enlarged view of the through-hole 38. Each of thethrough-holes 38 is plated at its inner wall with gold. In other words,each of the through-holes 38 is coated at its inner wall with a goldplating layer 39. Each of the through-holes 38 is filled with thetransparent molded-resin 35 with its inner wall being coated with thegold plating layer 39. As an alternative, each of the through-holes 38may be filled with a resin other than the transparent molded-resin 35.

[0077] An adhesion force between the gold plating layer 39 coating thethrough-holes 38 therewith and the transparent molded-resin 35 (oranother resin) covering the gold plating layer 39 therewith isrelatively small. In other words, the gold plating layer 39 and thetransparent molded-resin 35 (or another resin) make contact with eachother through such an adhesion force that heated moisture can bedischarged externally of the semiconductor device 30 through a small gapformed between the gold plating layer 39 and the transparentmolded-resin 35 (or another resin).

[0078] Thus, an interfacial surface between the gold plating layer 39and the transparent molded-resin 35 (or another resin) acts as a paththrough which moisture can pass.

[0079] Accordingly, when the semiconductor device 30 is heated in a stepsuch as a re-flow step and hence moisture contained in the transparentmolded-resin 35 expands, the expanding moisture goes forward along aninterfacial surface between the gold plating layer 39 and thetransparent molded-resin 35, and then, discharged externally of thesemiconductor device 30 through the through-holes 38.

[0080] As having been explained so far, the resin-sealed typesemiconductor device 30 in accordance with the second embodiment allowsthe moisture contained in the semiconductor device 30 to escapeexternally of the semiconductor device 30 through the through-holes 38,and can avoid from being cracked and peeled off due to the expansion ofthe moisture contained in the semiconductor device 30.

[0081] In the above-mentioned embodiment, a noble plating layer such asa platinum plating layer or a palladium plating layer may be used inplace of the gold plating layer 39.

[0082] [Third Embodiment]

[0083] Hereinbelow is explained a semiconductor device in accordancewith the third embodiment, with reference to FIGS. 3A to 3C.

[0084] When a metal wiring formed on a printed wiring board is platedwith a metal, a solder resist is first coated in a region which is notto be plated, and then, a metal wiring formed on a printed wiring boardin a region where a solder resist is not coated is plated with a metal.This process can be applied to the fabrication of the semiconductordevice in accordance with the third embodiment.

[0085] In the semiconductor device in accordance with the thirdembodiment, there is intentionally formed, on the printed wiring board11, a first region where a solder resist is not to be formed, apart froma second region where a solder resist is not to be coated in view ofdesigning a wiring pattern. The first area is formed such that a metalwiring to be formed in the first area and plated with a metal extendsexternally beyond the transparent molded-resin 15.

[0086] Hence, thereafter, a metal wiring formed in the second area isplated with a metal. The thus formed interfacial surface between thetransparent molded-resin 15 and a metal plating layer coated around themetal wiring can act as a path through which moisture contained in thesemiconductor device escapes externally of the semiconductor device,similarly to the interfacial surface formed between the metal wirings 17a, 17 b, 17 c and 17 d and the transparent molded-resin 15 in the firstembodiment.

[0087] Since a solder resist is composed of a resin similar to themolded resin, such as epoxy, an adhesion force between a solder resistand the molded resin 15 is relatively high. Accordingly, when moisturecontained in the semiconductor device is to escape externally of thesemiconductor device, the moisture passes through an interfacial surfacewhere a small adhesion force exists, namely, an interfacial surfacebetween a metal plating layer with which a metal wiring is plated, andthe molded resin 15.

[0088] In accordance with the semiconductor device, similarly to thesemiconductor device 10 in accordance with the first embodiment, itwould be possible to allow moisture contained in the semiconductordevice to escape externally of the semiconductor device, and hence,prevent the semiconductor device from internally cracking and/or peelingoff which would be caused by expansion of moisture contained in thesemiconductor device.

[0089] Any one or more of the metal wirings 17 a, 17 b, 17 c and 17 d inthe first embodiment may be formed as a metal wiring or metal wiringscoated with a metal plating layer in accordance with the thirdembodiment.

[0090] The above-mentioned first to third embodiments may be reduced topractice alone or in combination.

[0091] Specifically, there may be currently formed both the metalwirings 17 a, 17 b, 17 c and 17 d in the first embodiment and a metalwiring coated with a metal plating layer in the third embodiment. As analternative, there may be currently formed both the metal wirings 17 a,17 b, 17 c and 17 d in the first embodiment and the through-holes 38 inthe second embodiment. As an alternative, there may be currently formedboth the through-holes 38 in the second embodiment and a metal wiringcoated with a metal plating layer in the third embodiment. As analternative, there may be currently formed all of the metal wirings 17a, 17 b, 17 c and 17 d in the first embodiment, the through-holes 38 inthe second embodiment, and a metal wiring coated with a metal platinglayer in the third embodiment.

[0092] While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

[0093] The entire disclosure of Japanese Patent Application No.2001-232184 filed on Jul. 31, 2001 including specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A semiconductor device comprising: (a) a printedwiring board; (b) a semiconductor chip mounted on said printed wiringboard; (c) a molded resin formed on said printed wiring board, coveringsaid semiconductor chip therewith; and (d) at least one metal wiringformed on said printed wiring board and extending externally beyond saidmolded resin, said metal wiring being plated with a metal having a smalladhesion force with said molded resin, wherein an interfacial surfacebetween said metal and said molded resin acts as a path through whichmoisture contained in said semiconductor device escapes outside whensaid semiconductor device is heated.
 2. The semiconductor device as setforth in claim 1, further comprising a solder resist formed in an areaother than an area plated with said metal.
 3. The semiconductor deviceas set forth in claim 1, wherein said -metal is a noble metal.
 4. Thesemiconductor device as set forth in claim 3, wherein said metal isgold, platinum or palladium.
 5. The semiconductor device as set forth inclaim 1, wherein said molded resin is a transparent resin.
 6. Asemiconductor device comprising: (a) a printed wiring board; (b) asemiconductor chip mounted on said printed wiring board; and (c) amolded resin formed on said printed wiring board, covering saidsemiconductor chip therewith, wherein said printed wiring board isformed with at least one through-hole, said through-hole is filled withsaid molded resin or another resin with said through-hole being platedat an inner wall thereof with a metal having a small adhesion force withsaid molded resin or said another resin, and an interfacial surfacebetween said metal and said molded resin or said another resin acts as apath through which moisture contained in said semiconductor deviceescapes outside when said semiconductor device is heated.
 7. Thesemiconductor device as set forth in claim 6, further comprising asolder resist formed in an area other than an area plated with saidmetal.
 8. The semiconductor device as set forth in claim 6, wherein saidmetal is a noble metal.
 9. The semiconductor device as set forth inclaim 8, wherein said metal is gold, platinum or palladium.
 10. Thesemiconductor device as set forth in claim 6, wherein said molded resinis a transparent resin.
 11. A semiconductor device comprising: (a) aprinted wiring board; (b) a semiconductor chip mounted on said printedwiring board; and (c) a molded resin formed on said printed wiringboard, covering said semiconductor chip therewith, wherein said printedwiring board has a first area in which a solder resist is not formed,said first area is formed such that a metal wiring formed in the firstarea and plated with a metal extends externally beyond said moldedresin, and an interfacial surface between said metal wiring and saidmolded resin acts as a path through which moisture contained in saidsemiconductor device escapes outside when said semiconductor device isheated.
 12. A semiconductor device, comprising: (a) a printed wiringboard; (b) a semiconductor chip mounted on said printed wiring board;(c) a molded resin formed on said printed wiring board, covering saidsemiconductor chip therewith; and (d) at least one metal wiring formedon said printed wiring board and extending externally beyond said moldedresin, said metal wiring being plated with a first metal having a smalladhesion force with said molded resin, wherein said printed wiring boardis formed with at least one through-hole, said through-hole is filledwith said molded resin or another resin with said through-hole beingplated at an inner wall thereof with a second metal having a smalladhesion force with said molded resin or said another resin, and aninterfacial surface between said first metal and said molded resin andan interfacial surface between said second metal and said molded resinor said another resin act as paths through which moisture contained insaid semiconductor device escapes outside when said semiconductor deviceis heated.
 13. A semiconductor device comprising: (a) a printed wiringboard; (b) a semiconductor chip mounted on said printed wiring board;and (c) a molded resin formed on said printed wiring board, coveringsaid semiconductor chip therewith, wherein said printed wiring board hasa first area in which a solder resist is not formed, said first area isformed such that a metal wiring formed in the first area and plated witha metal extends externally beyond said molded resin, said printed wiringboard is formed with at least one through-hole, said through-hole isfilled with said molded resin or another resin with said through-holebeing plated at an inner wall thereof with a second metal having a smalladhesion force with said molded resin or said another resin, and aninterfacial surface between said metal and said molded resin and aninterfacial surface between said second metal and said molded resin orsaid another resin act as paths through which moisture contained in saidsemiconductor device escapes outside when said semiconductor device isheated.